Pressure-sensitive adhesive tapes are used for many diverse applications including, for example, marking, holding, protecting, sealing and masking purposes. These tapes comprise a backing, or other substrate, and a pressure-sensitive adhesive. Pressure-sensitive adhesives used in pressure-sensitive adhesive tapes generally adhere with no more than applied finger pressure and often stay tacky for months or years. Pressure-sensitive adhesives exert a strong holding force and should be removable from a smooth surface without leaving a residue.
In the medical field, pressure-sensitive adhesive tapes may be used, for example, to secure a wound dressing or to restrict movement of a joint or limb. It is important that the pressure-sensitive adhesive tape adhere well to skin without causing skin damage on removal.
Electrical tapes typically comprise a pressure-sensitive adhesive applied to a plasticized polyvinyl chloride backing or a polyethylene or rubber film backing. Electrical tape is used to insulate, hold, reinforce and protect electrical wires. Other uses include identifying wires in electrical circuitry, and protecting terminals during manufacture of electrical circuit boards.
Packaging applications require a large variety of tapes for uses such as closing packages, protecting labels, sealing packages from moisture, and strapping and bundling loose parts. Packaging tapes are subjected to continuous shear and low angle peel forces. Generally, if the adhesive mass is of low cohesive strength, it fails in shear; if the shear resistance is improved by adding firmness to the adhesive, it has a tendency to be less tacky and fail adhesively.
Pressure-sensitive adhesives require a delicate balance of viscous and elastic properties which result in a four-fold balance of adhesion, cohesion, stretchiness and elasticity. Pressure-sensitive adhesives generally comprise polymers that are inherently tacky or polymers that are tackified by the addition of tackifying resins.
Major classes of pressure-sensitive adhesives include tackified natural rubbers; synthetic rubbers such as butyl rubber; and tackified linear, radial, star, branched and tapered block copolymers such as styrene-butadiene, styrene-ethylene/butylene and styrene-isoprene; polyvinyl ethers; acrylics, especially those having long chain alkyl groups; poly(1-alkene)s (also referred to as poly-.alpha.-olefins); and silicones.
Polyolefin catalyst systems (i.e., Ziegler-Natta (ZN) and metallocene) have made it possible to synthesize high molecular weight poly(1-alkene) pressure-sensitive adhesives including homopolymers of C.sub.6 to C.sub.10 poly(1-alkenes).
Another type of poly(1-alkene) material, by-products of isotactic polypropylene that are described as atactic copolymers of C.sub.3 -C.sub.6 and C.sub.3 -C.sub.8 with molecular weights up to 50,000, have found uses as hot melt adhesives. These copolymers also make pressure-sensitive adhesives when mixed with tackifiers.
Pressure-sensitive adhesives comprising blends of poly(1-alkenes) and flow-control agents are used to protect surfaces such as automobile paint finishes and may be removed without leaving residue.
Radiation crosslinking of poly(1-alkene) homopolymer or copolymer compositions (both Ziegler Natta-catalyzed and metallocene-catalyzed) has been accomplished.